This Phase-l SBIR project, of a Fast Track pair, will provide concept testing, computer simulation studies, laboratory-based hardware emulation and a final specification for the final scanner to be constructed in the Phase ll SBIR project. The result of this Fast Track effort is intended to be used as the foundation, starting specifications and design for the construction and clinical testing of a pair of advanced, second-generation, "Ultrasound CT(tm)" breast cancer detection and diagnostic scanners. No construction of scanner components will be done during Phase-l. During Phase-ll, these two second generation scanners would be installed at Mayo Clinic and at the University of California at San Diego Hospital. These second generation scanners include improved features over TechniScan's first generation scanner that was installed in a local cancer center in August 2004. The first generation scanners consist of two opposing, but parallel, 2-D transducer arrays that rotate about a pendent breast in a water tank. The arrays also are moved vertically after each 360 degree rotation. Inverse Scattering, 3-D, Tomographic images were computed for sound speed and acoustic attenuation. Since August 2004 new transmit and receiver arrays are being incorporated. To these capabilities the second generation scanner adds: (1) improved inverse scattering in-plane spatial resolution and signal to noise ratio by beam shading and by relative rotation between transmit and receiver arrays; (2) improved inverse scattering spatial resolution by tilting the arrays in a vertical direction; and (3) improved reflectivity imaging by adding a commercial OEM beam former. [unreadable] [unreadable]